Natural killer (NK) cells have been proposed to play an important role in recovery and/or protection from different viral infections. We have recently demonstrated that a non-B, non-T, non- monocytic nonadherent peripheral blood leukocyte subset which bears HLA-DR, and D44 molecules on its surface produces IFN- alpha in response to cytomegalovirus-infected fibroblasts (CMV- FS4) and also provides vital accessory help to CD16 (Leu-11b)+, HLA-DR- NK cells allowing them to mediate lysis of CMV-FS4. These nonadherent HLA-DR+ cells have not yet been characterized and phenotypic markers other than HLA-DR and D44 antigens present on the surface of this cell subset are unknown. Since HLA-DR and D44 antigens are not specific markers being present on a heterogenous cell population, we will attempt to characterize this nonadherent HLA-DR+ cell subset by: i) Enrichment through negative selection and positive selection (by cell sorter) techniques followed by morphological, biochemical, and phenotypical marker analysis. ii) Producing new monoclonal antibodies to identify new phenotypic markers (other than HLA-DR and D44) present on this nonadherent HLA-DR+, D44+ cell subset. Experiments will be performed to determine whether lymphokines other than Interferon-alpha are produced by this cell subset. We will also attempt to maintain and/or grow this cell subset in vitro and determine whether markers of activation appear. The precise role of Interferon-alpha in spontaneous killing of CMV-FS4 by peripheral blood mononuclear cells will also be determined. The long rang objective is to apply the knowledge acquired from these studies to analyze the possible role of this nonadherent HLA-DR+ cell subset along with NK cells in resistance to viral infections.